Chronic SO2- and NOx-Pollution Interferes with the K+ and Mg2+ Budget of Norway Spruce Trees

j. Plant Physiol. Vol. 148. pp. 276-286 (1996)

Chronic S02- and NOx-Pollution Interferes with the K+ and Mg 2+ Budget of Norway Spruce Trees STEFAN SLOVIK 1

1

Julius-von-Sachs-Institut flir Biowissenschaften mit Botanischem Garren der Universitat Wlirzbutg, Lehrstuhl flir Botanik I, Mitderer Oallenbergweg 64, 0-97082 Wlirzburg, Germany

Received June 24, 1995 . Accepted October 30, 1995

Summary

Quantitative data concerning the impact of chronic S02 and NO x (= N0 2 + NO) pollution at ambient concentrations on the nitrogen (N org), sulphur (Sorg), K+ and Mg2+ budget of Norway spruce trees growing in synchronized monocultures are summarized. (i) Stomatal S02 and NO x uptake rates, (ii) epicuticular S02 and NO x deposition rates (including aerosol deposition), and (iii) sulphur and nitrogen deposition rates via acid precipitation are considered. Atmospheric S02 and N0 2 concentrations required to supply the total S- and N-demand of growing spruce trees are deduced. Based on the total Sorg and N org demand (i) of whole spruce trees or alternatively, (ii) of harvested trunk wood per monoculture turnover, critical load rates for sulphur and nitrogen are deduced and compared with stomatal, epicuticular and ombrogenic sulphur and nitrogen deposition rates in spruce forests of central Europe. Reductive and oxidative S02 detoxification pathways in spruce needles are quantified. Measured SOr and NOx-dependent cation throughfall rates from spruce canopies are compared with the additional cation demand rates of spruce stands after stomatal uptake of S02 (for S042- neutralization purposes) or of NO x (for avoidance of [K+ or Mg2+]: N org dilution). Chronic SOrpollution is 2.0 to 2.6 times more phytotoxic than equally high N0 2 concentrations in air. The here presented own data, which are available for different site elevations and tree age classes, are discussed within the context of «spruce decline».

Key words: Air pollution (502, N02 , NO), Cation competition (IC, Mj+), Critical load (50/-, NOj -), Chronical deposition (aerosol, cuticle, stomata, precipitation), Detoxification (trace gases), Forest decline (Norway spruce, Picea abies fL.) Karst., Pinaceae), Tree nutrition (nutrient cycling). Abbreviations: Aspec = Specific needle surface area per kg needle dry matter [m 2 kg-lOW]; Cat = Any cation species (K+, Mg 2+ etc.); G H20 = Stomatal H 20 conductance of mean needles [mmol H 20 m- 2 needle surface s-I]; GP = Trunk growth period (= duration of the annual «vegetation period») [da- I]; h = Site elevation above the sea level [ma.s.!.]; J'gas = Specific stomatal trace gas uptake rate [j.lmolm- 2 needles d-1 (GP) (nPa Pa-I)-I]; lNo, = St?matal (N0 2 + NO) flux _~er unit needle surface [j.lmolm- 2 d- 1 (GP)]; ls0 2 = Stomatal S02 flux per Unit needle surface [j.lmol m needle surface d- 1 (GP)]; Lion = Measured canopy throughfall rate [mmol kg- I needle OW a-I]; Lo = Background leaching rate in clean air [mmolkg-I needle OWa- I]; L'jon = Specific ion leaching rate per needle dry matter [mmolkg- I OWa- 1 (nPa Pa-I)-I]; N org = Organic nitrogen compounds; [N0 2]a = Annual mean of the ambient N0 2 concentration in air [nPa Pa-I = ppb]; r = Pearson correlation coefficient [no dimension]; [S02] a = Annual mean of the ambient S02 concentration in air [nPa Pa-1 = ppb]; Sorg = Organic sulphur compounds; Srel = Relative within needles fraction of the annual stomatal S02 dose that is oxidized to accumulating [mol mol- I S02]; LCat = Stoichiometric sum of cation equivalents [Eq]; t = Stand (tree) age of synchronized spruce monocultures in years [a]; TP rel = Relative contribution of a regarded cation Cat to the charge balance ofsol-; z = Stoichiometric factor for different cation species (CatzS04).

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© 1996 by Gustav

Fischer Verlag, Sturrgart

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The fate of chronic S02 and NO z pollution Introduction

Norway spruce (Picea abies [L.] Karst.) is one of the economically most important tree species of the northern hemisphere (Schmidt-Vogt, 1986). For almost two decades, symptoms of canopy thinning, early needle senescence, «unusual" trunk increment growth rates (and dynamics) and at extreme sites even a local decline of spruce trees became apparent in central Europe. Possible natural and anthropogenic reasons for these observations are discussed (e.g. Zech and Popp, 1983; Wentzel, 1985; Z6ttl, 1986; Schulze, 1989; Hiitd, 1991; Kandler, 1994). In this communication, field data obtained for stomatal, epicuticular and ombrogenic (= via precipitation) sulphur and nitrogen deposition rates ate compared to the growth demand for sulphur (Sorg), nitrogen (N org), K+ and Mgz+ of initially healthy spruce monoculcures (i.e. before development of «decline" symptoms). Focussing for example on stomatal SOz uptake (cf. Fig. 1), generated (bi)sulfite anions may cause acute damage symptoms, which are out of the scope of this discussion, since observed SOz concentrations are usually toO small in the field (exceptions admitted). Still, chronic SOz uptake by needles forces

Fate of S02-pollution

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Interference with sulphur metabolism

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Cation supply from the soil Fig. 1: Overview of chronically activated detoxification (SOz -+ Sorg' or SOz -+ SO/-) and compensation pathways in spruce trees after long lasting S02 pollution at ambient S02 concentrations in the field. Concerning NO, (= N0 2 + NO), only reductive detoxification (NO, -+ N org) is observed in the field at ambient NO x concentrations.

277

reduction (SOZ ~ Sorg) or oxidation (SOZ ~ HzS04) of generated (bi)sulfite in the longterm (cf. Ziegler, 1975). This metabolic «bifurcation" of SOz detoxification pathways is absent at ambient annual means of NO z pollution in spruce forests (ca. 8 to 16 nPa NO z Pa- I = ppb; cf. Siovik et al., 1996 a). There is NOz-dependent N0 3 - accumulation in spruce needles only after fumigation with much higher NO z concentrations (200 to 500nPa NO z Pa- 1 = ppb) than those which occur in the field (Tischner et aI., 1988; Kaiser et aI., 1993). Generation of H 2S0 4 in the needle mesophyll activates pH-stat mechanisms, which mobilize base (OH-) and cations (Cat) as counterions of In the field, pH-statmechanisms are not overburdened (B6rtitz, 1969, Kaiser et al., 1991). Cations, which are sequestered into needle vacuoles together with accumulating (mainly K+; cf. Siovik et aI., 1996 c), are unavailable for growth. There is little retranslocation before needle abscission. Thus, cations immobilized in the vacuole (e.g. K ZS0 4) represent an additional cation loss in shed spruce needles, which would be absent in clean air. Similarly, there is additional cation leaching after absorption of SOz in spruce canopies (Slovik et al., 1996 b). Thus, chronic SOz pollution causes competition for cations, which is harmful mainly (i) at unfertilized or unlimed, poor stands if water soluble sulphate salts further leak from the soil matrix into the ground water, or (ii) if shed or leached cations, e.g. K+, are taken up by competitive plants or soil microorganisms. This lack of local nutrient recycling is dominant mainly at stands growing on acidic soils (case i), or if there is concomitant nitrogen deposition, which acts as a fertilizer of soil organisms (destruents) and of fast growing herbaceous plants (case ii). The by these plants incorporated cations become unavailable to spruce trees. Thus, cation deficiency or - alternatively - thinning of the canopy structure must be the consequence in the long-term. In contrast to SOz, NO z is quantitatively assimilated (NO z ~ Nor) in spruce needles (acute cell damage by NO z is omitteJ here; cf. Wellburn, 1990). Stomatal NO z uptake either induces additional tissue growth (if a raising N org content in spruce tissues is to be avoided), or it leads to an increase of the N org content in spruce tissues (if stimulation of growth is absent). In the first case, there is an additional cation demand for tissue growth if dilution of cations (~ cation deficiency) is to be avoided in the longterm (cf. Schulze, 1989). Also in the second case, there is an additional cation demand if the Cat: N org ratio is to be kept constant as it was in healthy spruce trees before onset ofNO z pollution, since a high and stable K+: N org ratio is an important parameter of pathogen tolerance and frost hardiness in the field. Thus, chronic SOz and NO x pollution both induce an additional cation demand, which would be absent in clean air, since stomatal trace gas uptake is - of course - not accompanied by an equivalent stomatal cation uptake. Concerning SOb this . cation equivalency is defined (i) by the relative sulphate formation percentage Sre! per unit of stomatal SOz uptake flux [mol SO/- mol-I SOZ] and (ii) by the relative contribution of different cations to the charge balance of vacuolar sulphate TPre! [Eq Cat Eq-l SOl-]; TP stands for «tonoplast symport». Concerning NO z (incl. NO), its cation equivalency is defined by the Cat: N org demand ratio for the growth of healthy spruce trees. In diis communication, the as yet men-

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278

STEFAN SWVIK

tioned expectations are quantified and discussed in the context of «spruce decline,), focussing only on chronic effects which develop after a couple of years. Materials and Methods A set of results of the author is presented here in the manner of a short review. Thus, the applied approaches are only briefly summarized here (c£ citations):

trunk bark, root wood, root bark, fine roots etc.) of healthy spruce trees growing in ageing monocultures at different site elevations were reconstructed on the basis of historical trunk yield tables after «Wiedemann" (cf. Schober, 1987), growth data after Vanselow (1951; c£ Schmidt-Vogt, 1986), morphometric data after Mette and Korell (1989) and supplementary morphometric field data (c£ Slovik, 1996 for derivarion of tissue growth scenaria [kg tissue DW ha -I a -I] and tests of data consistency).

Results

Stomatal trace gas uptake

Stomatal 502 and NOx uptake

Annual trace gas doses at six spruce stands in Hessen (Germany) were numerically integrated from 1984 to 1992 with high rime resolution (30 min; 17,520 integration steps per year). Meteorological field data, which served as the data basis for modelling stomatal conductances after Korner et al. (1995), and pollution data of SOz, NO z and NO were measured within spruce forests by the Hessische Landesanstalt rur Umwelt (Wiesbaden, FRG). Obtained annual doses from all available sites and years (= «site·years") were first standardized on a unit length of the trunk growth period GP [d a~l], since this «annual vegetation period" is the predominant time period with open stomata per year. Standardized quotients were then correlated versus the corresponding annual means of trace gas concentrations of all site· years. Thus, statistical functions became available, which allow the estimation of annual stomatal trace gas doses of spruce needles in the field if only (i) annual means of trace gas concentrations and (ii) the length of the growth period GP are available; c£ Siovik et al. (1995) and Siovik et al. (1996 a) for details: substomatal concentrations, canopy effects, data validation etc. Epicuticular 502 and NOx absorption (incl. aerosol deposition)

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Annual canopy throughfall and precipitation rates of and N0 3 -, and of cations (NH 4 +, K , Mgz+ etc.), measured at the same sites in Hessen where stomatal trace gas fluxes were integrated (c£ above), are available after Balazs (1991). Throughfall data, that originate from canopy surfaces themselves, were first corrected for expected artificial concentration increases after evaporation of intercepted precipitation water and then correlated with concomitantly measured annual means of SOz or NO z concentrations in air. Linear correlation and regression analysis was performed also for cations vs. (SOz or NO z) in order to identify the «mean" ionic composition pattern of trace gas-dependent spruce canopy leachates in the field; cf. Siovik et al. (1996 b). Nutrient analysis data

After pressure ashing of samples, analysis of metal cations (K+, Mi+, u. a.) and of total sulphur was performed by inductively coupled plasma OCP) atomic emission spectrophotometry (Model JY 70 PLUS, ISA Jobin-Yvon, France) with an automatic sample injector (Gilson model 222, Villiers Ie Bel, France). The carbon and nitrogen content of spruce tissues was determined by element analysis (CHNO-Rapid, Heraeus, Hanau, Germany). After hot water extraction of spruce tissues, anions (SOl-, N0 3 -) were detected by isocratic anion chromatography (HPLC; Ionenchromatograph IC 100, Biotronik, Maintal, FRG). Tissue analysis data from healthy spruce trees growing in Wiirzburg (Botanical garden) were taken as references. Tissue growth rates in ageing spruce monocultures

As references, typical growth and turnover rates of all important tissues and organs (needles, branch wood, branch bark, trunk wood,

The specific stomatal uptake dose of trace gases, given in Ilmol (S02 or NO x) m- 2 needle surface day-I (growth period GP) (nPa Pa-I)-I annual mean of concentration in the air, depends on the annual trace gas pollution pattern measured in spruce forests «
1.5

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Fig. 2: Kinetics of the annual SOz, NOz, NO and 0 3 pollution pattern in Norway spruce forests (relative units), measured in central Europe (pooled data from 6 sites in Hessen, FRG). Bold lines represent monthly means of n=45 site .years. Thin lines denote standard deviations (SD) of these field data (after Siovik et al., 1996 a).

279

The fate of chronic SOz and NO z pollution

OL--'---'---------'----'---------'----'---------'---'-----'---'---'---'--' Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Time [months]

Fig, 3: Typical annual kinetics of the stomatal canopy conductance [mmol HzO m- z total needle surface S-I] of Norway spruce canopies in central Europe (Hessen, FRG). Bold lines indicate monthly means (± SO, thin lines) of results from n =45 pooled site·years. The given data already consider that the stomatal conductance of mean needles of spruce canopies is only ca. 0.32 times the needle conductance of exposed needles (canopy effects!). The stomatal SOz conductance is (0.51 to 0.53) times, and the stomatal NO z conductance is (0.58 to 0.63) times the HzO conductance; modelling of stomatal conductances after Korner et al. (1995) was based on meteorological field data in Hessen (after Slovik, 1996; cf. also Slovik et al., 1995, 1996a).

ticular» deposition), and which by 30 % (100 %·1.0/3.3) is possible only if stomata are open mainly (not only) in the summer at day hours (= stomatal uptake of SOz and NO x)' Since both, stomatal trace gas uptake and «epicuticular» trace gas deposition, share (i) similar deposition resistances (unstirred boundary layers, «canopy effects», impact of wind velocities), and (ii) a common water dissolution step (in cell wall water within the needle mesophyll, on wet canopy surfaces or first in fog water before aerosol deposition), similar statistical deposition functions are not only expected in the field, but indeed observed (cf. Fig. 4). Fig. 4 allows the estimation of «typicah, and N0 3 - throughfall rates per unit of needle dry matter if only annual means of SOz and NO z pollution are known.

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Epicuticular trace gas and aerosol deposition In Fig. 4 stomatal uptake rates of SOz and NO x are compared with spruce canopy throughfall rates of and N0 3 - as depending on annual means ofSO z or NO z concentrations in air, measured at the same sites in Hessen (cf. Slovik et aI., 1996 b). Compared with stomatal uptake functions, «epicuticulan, sulphur and nitrogen deposition functions (including aerosol deposition) show a congruent shape of trace gas dependency (cf. Fig. 4). Both, stomatal and «epicuticulan, nitrogen deposition, show a «compensation point» at (5 to 7) nPa NO z Pa- 1 (cf. arrows in Fig. 4). Comparison of obtained regression slopes in Fig. 4 (including NH 4 + throughfall data versus NO z pollution data; not shown here) yields ca. 2.3 times higher trace gas dependent throughfall rates of or N0 3 - (plus NH 4 +) per unit of trace gas pollution than corresponding specific stomatal SOz or NO x uptake rates (cf. Siovik et aI., 1996 b). Integration of the area below the «typical>, stomatal conductance curve in central Europe after Fig. 3 allows the quantification of the ratio of total annual hours (8760 h a-I) per annual hours with «open» stomata. This ratio equals ca. 2.3 h h- 1 for SOz and for NO z (cf. Siovik et aI., 1996 a, b). Thus, there seems to be a concomitant SOz and NO x deposition into spruce canopies, which by 70 % (= 100%·2.3/3.3) occurs all the year at day and night (= «epicu-

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estimation of stomatal SOz and NO x (NO z + NO) uptake fluxes in the field if (i) annual means of SOz and NO z pollution, and (ii) the annual length of the growth period GP [da-I] are known. The latter depends on the geographical site elevation and on the site latitude of northern and central Europe (cf. Wiersma, 1963).

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Fig, 4: Stomatal SOz and NO x (= NO z + NO) uptake rates by, and epicuticular SOz (-+ SO/-) and NO x (-+ N0 3 -) deposition rates in Norway spruce canopies as depending on the SOz or NO z concentration in air (pooled available data since 1984 from 6 spruce sites in Hessen, FRG). Epicucicular deposition rates after Balazs (1991; cf. Siovik et aI., 1996 b) are given in mmol (SO/- or N0 3 -) kg-I needle OW year-I. Error bars denote standard deviations (SO for n =3 or 4 plots per site). Parameters of epicuticular trace gas deposition rates (LS04 LN03 ) are r = Pearson correlation coefficient [no dimension], Lo = intercept [mmol kg-lOW a-I] and L'ion = slope [mmol kg- I needle OW a-I (nPa Pa-I)-I annual mean of trace gas pollution]: Lso,=f([S02LJ r=0.701"· Lo = 3. II ±3.09 L'so,= 1.682±0.428 LNo,=f([N0 2J.) r=0.489· Lo=-4.10±3.85 L'N03 =0.753±0.347 Data of annual stomatal SOz and NOx uptake rates in l1mol SOz or NO x (= NO z + NO uptake) per m Z total needle surface, and stan-

dardized per day (d) of the annual trunk growth period GP [da-I], after Slovik et al. (1995, 1996 a). Parameters of stomatal trace gas uptake rates 050" JNO) are: r = Pearson correlation coefficient [no dimension], b = intercept [l1mol m -z needle surface d -I growth period] and gas = slope [l1mol m -z needle surface d-I growth period (nPa Pa-I)-I annual mean of trace gas pollution]:

r

Jso,=f([S02JJ r=0.909···· b= 0.647±0.114 rso,=0.157±0.01l JNO, =f([N0 2],) r=0.903···· b=-3.309±0.401 rNO, =0.477±0.035

The specific needle surface A,pec of spruce needles equals (11 to 13) m Z total surface kg-I needle OW. The dependency of the annual growth period GP [da-I] on the site elevation in central Europe (latitude"" 50' northern hemisphere) is given in Table 2 (cf. Wiersma, 1963).

280

STEFAN SLOVIK

Table 3: «Necessary» NO z and S02 pollution (annual means) that

Data basis ofannual nutrient demand rates As a reference, total nutrient contents (N org , Sorg' K+, Mg2+) of different tissues from healthy spruce trees growing in Wlirzburg (cf. Table 1) were interrelated with «typical» site- and stand age-dependent canopy, trunk and root tissue growth rates of healthy spruce monocultures in the field (cf. Siovik, 1996) in order to obtain total annual nutrient demand rates of entire spruce trees (i) either on a hectare basis, or (ii) per unit stock of needle dry matter (= interface to stomatal S02 or NO x uptake rates after Fig. 4). Table 2 exemplifies results obtained for «typicah> spruce growth rates focussing on the CO 2 balance (annual net photosynthesis, annual respiration [incl. e.g. root leaching], CO 2 fixation in dry matter) of spruce monocultures growing at different site elevations. Shown are annual CO 2 balance rates of entire spruce trees, but given on a needle dry matter basis. Results of the spruce growth model after Siovik (1996) are consistent with independent investigations.

Mere atmospheric nitrogen and sulphur supply Atmospheric S02 and NO x may serve as S- and N-sources for plant growth. In Table 3 N0 2 and S02 concentrations in and Mg2+ contents of different spruce tissues (Picea abies) analyzed in Wiirzburg (Botanical Garden) in 1991 (± SD; n = 50).

Table 1: Organic nitrogen (N org ), sulphur (Sorg),

Tissue or tree organ

K+

Org. nitrogen Org. sulphur Potassium

Magnesium Mg2 + [mmol kg'l] [mmol kg'l] [mmol kg'l]

5",g

K+

Green needles 652± 121 Brown needles 438± 92 Retranslocation 214± 44

25.2±9.9 16.8±2.9 8.4±3.0

122.9±32.2 82.0±14.1 40.9±35.2

31.1 ±6.8 37.6±5.1 -6.5±8.5

Branch bast Branch wood Root bast Root wood

14.9±7.4 3.9±O.9 11.4± 1.6 5.6±2.3

99.0± 18.5 20.4± 4.2 139.1 ±21.4 77.5±33.5

37.3±6.6 6.4± 1.6 43.9±9.5 15.2± 1.4

No,g

[mmol kg'l]

Picea abies

537±119 133± 27 458± 63 273± 22

Table 2: Annual CO 2 fixation (dry matter formation), net photo-

synthesis and respiration (incl. root leaching) of Norway spruce trees growing at different site altitudes. Data of whole trees are given on a needle dry matter basis [mol CO 2 kg'l needle DW a-I]. The mean length of the annual trunk growth period is estimated after Wiersma (1963). Percentage data of respiration and CO 2 fixation are given on a net photosynthesis basis = 100 %; data were calculated after Slovik (1996). Growth CO 2 Site net photo- respi- respi- CO 2 synthesis ration ration fixation altitude period fixation I [d a-I] [mol C kg- a-I] [m] [%] [0/0] 10 400 800 1200 1600 2000

222 200 176 154 130 108

41.0±4.2 40.2±4.3 39.6±4.4 38.5±4.4 36.5±4.3 33.6±4.1

118 106 93 82 69 57

77 66 53 44 32 23

65 62 57 54 46 40

35 38 43 46 54 60

formally supplies - after stomatal uptake - the entire No,g or So,g demand of ageing Norway spruce trees growing in the field. Shown are amplitudes from young trees (t "" 5 years; first value) up to old trees (t "" 120 years; second value). Data were calculated after Slovik (1996). Site elevation [ma.s.!.]

S02 [nPa Pa- I = ppb]

N0 2 [nPa Pa- I = ppb]

10m 1000 m

~28-17

~340-230 ~340-180

~

28-11

air (annual means) have been deduced, which would be sufficient to meet the total N org and Sorg demand of healthy spruce monocultures growing at two selected site elevations (ca. 10 and ca. 1000 m a.s.!.). Necessary S02 concentrations range from ca. 28 nPa S02 Pa,-I (= ppb S02) in very young s~ruce stands (ca. 5 years old) to only 17 or 11 nPa S02 Pa- in ca. 120 years old spruce stands. At lower elevations more S02 is <
Critical load rates for nitrogen and sulphur In natural spruce ecosystems growing in clean air, there are only small nitrogen losses via e.g. NH 3 or NO x emission into the air, or via e.g. N0 3 - leaching into the ground water. Only these nitrogen losses must be compensated in a balanced ecosystem (atmospheric input, Nrfixation e.g. by microorganisms). After harvesting of biomass in managed spruce forests, there is loss of carbon and nitrogen. This carbon loss should reduce the microbial soil activity and hence cause reduced N 2-fixation. Additionally, there is loss of nitrogen. Is this nitrogen loss in central Europe compensated by presently measured total nitrogen (= NH 4 + + N0 3 -) deposition rates via precipitation water? Is there a widespread excess supply of nitrogen in central Europe that forces spruce trees to «grow to death», i.e. to run into another - e.g. Mg2+ shortcut (cf. Schulze, 1989)? Necessary annual wet deposition rates of nitrogen and sulphur in order to resupply the mean annual N org and Sorg loss by harvesting spruce trunk wood at stands growing at varying site elevations are given in Table 4. Shown are mean annual values per a 120 years lasting monoculture turnover period; cf. Schober (1987). The mean annual nitrogen load (N0 3 - and NH 4 +) contained in precipitation water at six spruce sites in central Germany (State of Hessen) since 1984 equals only (421 ± 106) mol N ha-1 a-I (pooled data after Balazs, 1991). Thus, on an ecosystem level, there is a higher mean annual nitrogen loss by trunk wood harvesting

The fate of chronic S02 and NO z pollution

Table 4: Dependency of critical wet deposition rates (precipitation flux) (mol (or kg) ha- I a-I) of niuogen (N0 3 - + NH 4 +) and sulphur (SO/-) on the site elevation (m a. s.I.). Data are calculated from the cumulative N org and Sorg fixation in harvested uunk wood (= nuuient loss) per spruce monoculture turnover (cf. Slovik, 1996) using the nutrient contents given in Tab. I; S02 and NOrdependent epicuticular and stomatal S02 and N0 2 deposition tates (cf. Fig. 4) are omitted here (but cf. Tab. 5). Observed field data after Balazs (1991).

Site altitude (m a. s.l.] 10m 400m 800 m 1200 m 1600m 2000 m Observed

Critical load of nitrogen

Critical load of sulphur

[mol ha- I a-I] [kg ha- I a- I]

[mol ha- ' a-I] [kgha- I a-I]

921 823 724 626 527 428 421±106

12.9 11.5 10.1 8.8 7.4 6.0 5.9± 1.5

27.3 24.4 21.5 18.5 15.6 12.7 180±32

0.87 0.78 0.69 0.59 0.50 0.41 5.7± 1.0

Table 5: Total niuogen (N0 3 -, NH 4 +, NOb NO) and sulphur (SO/-, S02) wet deposition (precipitation rates) and dry deposition (stomatal uptake. epicucicular deposition) in spruce forests growing in Hessen (central Germany; pooled data from Biebergemiind in the Spessart mountains, Frankenberg at the Sauerland mountains, Fiirth in the Odenwald mountains, Grebenau at the Vogelsberg mountain, Konigstein in the Taunus mountains and Witzenhausen close to Kassel) as compared with the N org and Sorg demand of these spruce stands. Given is the range of available annual means (summary of data after Balazs, 1991; Siovik et aI., 1996a.b). Deposition component Stomatal uptake flux Epicuticular deposition Annual precipitation Toeal nutrient input Total growth demand Percentage of supply [%] Trunk wood growth demand Percentage of supply [%]

Nitrogen compounds [mol ha- I a-I] 14 - 178 o - 404 286 - 547 300 -1129 2211 -2680 13.6- 42.1 % 724 - 823 41.4- 72.9%

Sulphur compounds [mol ha- ' a-I] 32- 153 58- 485 136- 218 226- 856 67- 81 337-1057% 22- 24 1027-3567%

than there is concomitant resupply of nitrogen by wet deposition of N0 3 - plus NH 4 + (cf. Table 4). Consequently, chronic wet deposition of nitrogen alone presently still not even compensates the N org demand for harvested trunk wood in central Germany. The N org demand of trunk bark - if it is also harvested (not decomposing in the field) - is even as yet disregarded. Thus, considering time ranges up to centuries, there is no excess nitrogen burden via «acid rain» on managed spruce ecosystems, but instead a nitrogen deficit if epicuticular and stomatal NO z deposition (= «direw> NO z effects; cf. Fig. 4) would be disregarded. Only the wet deposition of sulphur exceeds the Sorg demand for trunk growth by roughly about one order of magnitude (Table 4). Table 5 balances the total nitrogen and sulphur uptake of spruce ecosystems (sto-

281

matal uptake, epicuticular deposition, precipitation) at six sites in central Germany. Results are compared (i) with the total annual N org and Sor demand of all growing tissues in spruce stands and (ii) wit~ the N org and Sorg loss via harvesting of trunk wood. The total nitrogen deposition rate at six spruce stands in central Germany supplies only (13.6 to 42.1) % of the total N org demand of whole spruce trees, and (41.4 to 72.9) % of the N org demand only of trunk wood growth (Table 5). If compared with absolute clean air (and N-free precipitation water), then this additional supply percentage would correspond to an excess nitrogen supply into unmanaged forests (trunk harvesting absent). But this conclusion is usually not sound, since the correct nitrogen balance of managed spruce ecosystems must at first compare the aboveground input and output of nitrogen in order to get a remainder that burdens the soil below. Similar to Table 4, in Table 5 there is no massive nitrogen, but only a massive sulphur burden of managed spruce ecosystems, which exceeds the annual Sorg growth demand of entire spruce trees by (337 to 1057) % - or by (1027 to 3567) % = (10 to 35fold) if compared with the Sorg loss via harvesting of trunk wood. 502 detoxification pathways in spruce needles

As yet, nitrogen and sulphur balances of native spruce stands have been presented (ecological aspect). Now, the nitrogen and sulphur budget of spruce needles after stomatal NO x or S02 uptake must be considered (physiological aspect). At ambient concentrations N0 2 is essentially assimilated to N org compounds, but not oxidized to accumulating N0 3 - (cf. Tischner et aI., 1988; cf. Kaiser et al., 1993). The situation is different concerning chronic SOz-pollution at ambient concentrations. After stomatal uptake and hydration of S02> sulfurous acid (H 2S0 3) and finally (bi)sulfite anions are formed in the needle mesophyll. In the longterm, (bi)sulfite is either assimilated to reduced sulphur compounds, or it ~s oxidized to. sulphate anions yieldin? sulphuric acid. Even 10 the Erzgebuge (ca. 30 nPa S02 Pa- ) only 1 % of the S02 flux taken up via open stomata is balanced by re-emission of H 2S (Kindermann et al., 1995 a, b). Other reduced volatile sulphur compounds (CS2> COS etc.) are not detectable products of reductive S02 detoxification in spruce needles. Also the reductive assimilation of S02 to organic sulphur compounds Sorg is an unimportant S02 detoxification pathway: Fig. 5 indicates that there is only a weak and small positive correlation of the total Sorg content of spruce needles (harvested in the Erzgebirge) with the sulphate content of these needles (cf. Slovik et al., 1996a). The intercept of the shown linear regression (Fig. 5) is close to the Sorg content of needles conharvested at sites with rather clean air and small tents in needles (25.2 mmol Sorg kg- 1 needle DW in Wiirzburg; cf. Table 1). The sulphate content of spruce needles correlates with observed ambient S02 concentrations (Kaiser et al., 1993; Hiive et al.. 1995; Slovik et aI., 1995). The slope of the linear regression function in Fig. 5 equals (0.103 ± 0.058) mol Sorg mol-) Thus, 9.3 % (= 100 %·0.103/1.103) of the total accumulating sulphur is reduced sulphur Sorg and 90.7 % (= 100 %·1.000/1.103) of the total accumulating sulphur is sulphate. Clearly, is the

sol-

sol-.

sol-

282

STEFAN SLaVIK

50

Cl

~

"0

Picea abies

40

E

oS til

al

c

20

...c

10

...c Q)

0

••

•••

Q)

'0

.. . .. .. .. ., .-.. • .,.

•

• • ~

30

Q)

=0

•

•

r =

. 0.274

•

Kahleberg (Erzgebirge)

CJ

'"(;

0

(/)

0

10

20

SO 4

2-

30

40

50

60

70

80

90

-,

content of needles [mmol kg ,

Fig. 5: Correlation of the organic sulphur content Sorg in ca. 3.3 year old spruce needles (= oldest available needles) versus the sulphate content of these needles from massively damaged spruce trees growing on the summit of the Kahleberg (Erzgebirge, East Saxony, FRG); n = 41 trees; the regression equation equals Sorg = (0.103 ± 0.058)·sol- + (26.0 ± 3.0); The weak correlation is significant (error probability P<5 %; r=0.274*); data afrer Slovik et aI_ 0996c).

Q;~

(/)~-",

c 0

with a low ratio [SOz].: GP, i.e. at sites with clean air and long growth periods at lower elevations (= high tree growth rates and Sorl\ demand rates) in Konigstein, Wiirzburg and Grebenau (all in central Germany), only Srel> "" 0.3 mol 50/- mol- I SOz ("" 30 % of the low stomatal SOz uptake rate) accumulate as sulphate, while - apparently - 70 % of the annual (small) SOz dose yields sulphur that can be exported via the phloem sap. In spruce needles growing in the mountains at high ambient SOz concentrations in the Erzgebirge and high [SOz] a: G P ratios in Hockendorf, Oberbarenburg and Kahleberg, (70 to 90) % of the stomatal SOz dose accumulates as 50/- in spruce needles (cf. Slavik et aI., 1995). Under these conditions, there is an apparent limitation of phloem loading with sulphur compounds that forces the accumulation of 50/- in spruce needle vacuoles. In the mountains with short growth periods GP [d a-I] there is grosso modo only a restricted number of days per year with open stomata and efficiently working bast (phloem) elements. The function of phloem cells depends on speciesdependent minimum temperatures (cf. Gamalei et al., 1994), that must be exceeded within the time interval GP. Wiersma (1963) reports a minimum temperature of +6·C (daily mean) as the best ecological representative for the quantification of annual (trunk) growth periods GP (i.e. with largely open stomata and with dominant assimilate transport flow in the phloem sap).

o (/)

.~~-

E

SOrdependent vacuolar cation sequestration

"0

o -E

.....alN ...

., 0

..

-a.(/)

:; til

-

"0

QioS a:

0.2

Picea abies

0.0 l£....o~~~...L..-~~~-'-_~~--'-~_~-J 0.00 0.05 0.10 0.15 0.20 [50 2 '.

:

-,

-,

GP [nPa Pa. ad 1

Fig.6: The relative sulphate formation Srel [mol (SOl-) mol- 1 (S02)) depends on the ratio [S02].: GP, since a high S02 pollution and a short trunk growth period GP [da-I] synergistically promores sulphate accumulation, vice versa; data points after Slovik et al. (1995); error bars are obtained using the GauB law of error propagation. The indicated eight sites are located in central Germany (Hessen: Konigstein, Grebenau, Witzenhausen; Northern Bavaria: Wiirzbutg, Schneeberg; Eastern Saxony: Hockendorf, Oberbarenburg, Kahleberg); cf. detailed site characterization afrer Slovik et al. (1995). The solid line is a least square fit to shown data. dominant detoxification product in spruce needles after chronic SOrpollution if acute needle damage by SOz is still largely absent. Massive Sorg accumulation is evident only in visually SOz-damaged spruce needles (cf. Grill and Esterbauer, 1973; Grill et al., 1979; Grill et al., 1980). In Fig. 6 the percentage Srel> [mol 50/- mol- l SOz] of in spruce needles accumulating 50/- [mmol 50/- kg-I needle OW a-I] per annual stomatal SOz dose [mmol SOzkg-1 needle OW a-I] is plotted versus the ratio of the observed ambient SOz concentration [SOz]. in air [nPa SOz Pa- I] to the length of the growth period GP [d a-I] (cf. Siovik et al., 1995). At sites

Gymnospermal needles accumulate more than 99 % of the analyzed sulphate not in the mesophyU apoplast (cf. PoUe et al., 1994), but in vacuoles (cf. Kaiser et al., 1989). Since there is no pH-decrease of needle homogenates even in spruce needles originating from the SOrpoUuted Erzgebirge (Bortitz, 1969; Kaiser et al., 1991), generated vacuolar H zS04 (cf. Kaiser et al., 1993) must have been neutralized in the field by H+ - Cat+ exchange at the tonoplast level. Correlation analysis data (Cat + vs. 50/- contents of needles) indicate that potassium is the main vacuolar cation that neutralizes sulphate in Wiirzburg and in the Erzgebirge (Table 6). The relative stoichiometric importance of potassium ranges from TPrel(K+) "" 0.59 Eq K+ Eq-I 50/- in Wiirzburg to TPrel(K+) "" 0.82Eq K+ Eq-I 50/- in the Erzgebirge (Kahleberg; cf. Table 6). Other significant~ correlating cations (Mgz+ and Zn 2 + or Mn z+ and AI +) play a minor role. Interestingly, there is no correlation between the Caz+ and the 50/- content in spruce needles at both sites (cf. Table 6). This has physicochemical reasons, since the oxalate content of spruce needle vacuoles is too high at the vacuolar pH value and the ionic strength of the cell sap for the coexistence of soluble CaS04 and extractable oxalic acid without vacuolar precipitation of Ca-oxalate (cf. Siovik et al., 1996 c). Fig. 7 shows the theoretical maximum contribution TPrel(Caz+) [Eq Caz+ Eq-l 50/-] to the vacuolar SO/neutralization in spruce needle vacuoles. Even at SOz polluted sites in the Etzgebirge there is no significant contribution of Caz+ to the neutralization of observed SOz-dependent 50/- accumulation (cf. Fig. 6). Still, there is concomitant accumulation of Ca z+ and 50/- in ageing spruce needles, but both accumulation rates are not causally interrelated:

283

The fate of chronic 502 and N0 2 pollution Table 6: Vacuolar cation sequestration stoichiometries TPre! [Eq Cat Eq-I SOl-] for different cation species as observed in the field in Wiirzburg (Botanical Garden, Lower Franconia, h = 200 m a. s.l., 5 to 10 nPa 502 Pa-I) or on the summit of the Kahleber (Erzgebirge, Ore mountains, h = 905 m a. s.l., ca. 30 nPa 50 2 Pa- R ). Blanks (-) indicate that this cation species did not correlate with the 50 2 content of needles at this site. There is no sol- -dependent Ca1+, Na +, Fe2 +, or Cu 2 + accumulation at both sites (but a needle age-dependent sol- and Ca2 + accumulation); data after Slovik et al. (1996 c). Cation

Wiirzburg (Bavaria) [Eq Cat Eq-I SOl-]

Kahleberg (Saxony) [Eq Cat Eq-I SOl-]

0.589±0.260 0.360±0.096 0.051 ±0.005

0.818±0.166 0.105±0.053 0.077±0.024

1.000±0.311

e:

.2

:;

0~

100

~

c..

E e: e: f0-

0

(J

+

N

0 .;:: ro

.~

ro

U

Ql

10

~::J

I

Picea abies

rr--!--,----.----,---.---.-~-r--.---,~_-,.__..__,_-__,

I~"',:~,~~:!,""""""""""""""'"""""",

Ql

.~ ro N

..

e:

~ 0

~

E ro E (5::J

::J

.

(J

ro

:2: > B

sol-,

The relative composition of counterions of that leak from spruce canopies in the field as statistically depending on ambient SOz concentrations in air, is given in Table 7. In contrast to vacuolar cation data given in Table 6, Ca2+ compensates ca. 40 % (eq.) of and is therefore the dominant cation that is «extracted» from spruce canopies after chronic SOz pollution « SOz absorption). concentration Thus, ca. 40 % of the SOz-dependent increment in the spruce canopy throughfall is gypsum (CaS04)' Potassium contributes only by about 26 % to the from spruce stoichiometric cation balance of leachin~ canopies (Table 7). Al3+, Mgz+ and Fe + play only a minor role. Since H 30+ concentrations in the canopy throughfall did not correlate with ambient SOz (or NO z) concentrations in air, deposited SOz must have been fully neutralized by Cat+ - H 30+ exchange at spruce canopy surfaces or by dissolution of alkaline dust, ash etc. particles deposited onto spruce crown surfaces (Slovik et al., 1996 b). Concerning NOz, the situation is different (cf. Table 7). With increasing NO z concentration in air, leaching of K+ from spruce canopies is strongly reduced (consumption by nitrogen-fertilized epiphytic mosses, lichens etc.?). The NH 4+ throughfall rates parallel increasing NO z concentrations, but there was no correlation between NH 4+ leaching rates and ambient SOz concentrations, i.e. no codeposition of (NH4hS04 was identified (Slovik et aI., 1996 b). It may be assumed that increased throughfall rates of NH 4+ at elevated NO z concentrations in

sol-,

sol-

sol-

....... Kahleberg.~

en

'xro

1.000±0.176

Trace gas-dependent cation leaching from spruce canopies

0.1

o

10

20

30

40

50

60

70

80

90 100

Sulphate content of the needles [mmol kg"l

Fig.7: Maximal relative contribution of Ca 2 + to the vacuolar solneutralization that is possible without vacuolar precipitation of insoluble Ca-oxalate c!Jstals. This theoretical maximum percentage TPre! (Ca2 +) [mol Ca + mol SOl-] was calculated based on (i) the pK. values and amount of soluble oxalic acid in needles, (ii) on the pH value of needle homogenates ('" pH of vacuolar sap) and (iii) on the solubility product K.ol = 2.56· 10- 9 (kmol m -3)2 of Ca-oxalate. Using the Debye-Hiickel-Onsager theory, K.ol was recalculated for ionic strengths of needle extracts; cf. Slovik et al. (1996 c). Solid lines indicate the interval of occurring sol- concentrations in needle samples from Wiirzburg and the Kahleberg (Erzgebirge). Dashed lines are extrapolations. Filled symbols indicate the mean sulphate contents in needles at both sites. Arrows indicate that at needle sulphate contents below 5 mmol sol- kg-I needle DWTP rel (Ci+) rapidly exceeds 30 % and reaches 100 % at ca. 2 mmol sol- kg-I needle DW Only below ca. 5 mmol sol- kg- I needle DW it is possible to consume ci+ for sol- neutralization purposes in needle vacuoles without precipitation of Ca-oxalate.

sol-

There is no correlation of Ca2+ vs. if pseudocorrelations, caused by pooled analysis data from all needle age classes (cf. Hiive et al., 1995), are thoroughly avoided (cf. Slovik et aI., 1996c).

Table 7: Results of linear correlation and regression analysis of cation leaching rates Lion from Norway spruce canopies in the field (pooled data since 1984 from six stands in Hessen, FRG) vs. concomitantly measured annual means of 502 or N0 2 concentrations in air [nPa Pa- I = ppb]. Only significant correlations are shown. The regression intercept Lo [mmol Cat kg-I needle DWa- l ] estimates the background leaching rate in «clean» air (extrapolation to zero). The regression slope L'ion [mEq Cat kg-I needle DWa-1 (nPa gas Pa-I)-I] is the specific trace gas-dependent canopy leaching increment. Slopes and intercepts are given ± standard errors (SE). Calculated percentage data (± SE) balance the ion stoichiometry of L'ion and therefore estimate the «mean» ionic composition of trace gasdependent cation leachates from spruce canopies in the field; data after Slovik et al. (1996b; cf. Balazs, 1991). Ion

H

Correlation Intetcept Lc Slope L'ion coefficient [mmol kg-I a-I) [mmol kg-I a-I ppb- 1]

Sulphur dioxide 0.435* 0.497* 0.764**** Mg2 + 0.404* Fe3+ 0.629**

Ca2 + K+ AI}+

3.52± 18.85± 0.05± 0.25± 0.04±

3.96 4.30 0.53 1.26 0.15

1:Cat+ -

Nitrogen dioxide K+ 0.475* NH 4 + 0.642** Mn 2 + 0.484* Zn 2 + 0.562* 1:Cat+ -

48.69± 10.05 -13.38± 7.00 -1.03± 2.78 -0.35± 0.14

Percentage

[0/0]

1.058±0.547 0.680±0.297 0.525±0.111 0.308±0.174 0.099±0.031

39.6± 20.5 25.5± II.l 19.7± 4.2 11.5± 6.5 3.7± 1.2

2.670±0.784

100.0± 29.4

-1.895±0.906 1.711±0.616 1.074±0.501 0.054±0.024

-200.7± 96.0 181.2± 65.2 113.8± 53.1 5.7± 2.5

0.944± 1.205

100.0± 127.6

284

STEFAN SWVIK

air are caused by the reduction of at first generated HNO z (or HN0 3) to NH 4 + (NO x -+ HNO z(3) -+ NH 4 + by epiphytic plants?), but this question still remains open.

NOx-dependent cation demand Stomatal uptake of NO x (NO z and NO) causes an additional cation demand if both, (i) dilution of cations (NO x consumed for growth), and (ii) increase of the N org : Cat + ratio (NO x not consumed for growth) are to be avoided in the longterm. There is an additional cation demand of about 0.2 mol K+ mol- 1 NO x and ca. 0.06 mol Mg2+ mol-1 NO x, which is only slightly dependent on the site elevation (cf. Table 8). Data are given on a whole tree basis.

Trace gas-dependent potassium and magnesium depletion The NOx-caused cation demand (Table 8) can be compared with the SOz-caused cation demand (Table 6) regardformation percentage Srel per SOzing also the relative uptake flux (cf. Fig. 6). Results of this comparison are given in Table 9, which summarizes the «necessary" NO z and SOz concentrations in air (annual means) that cause - after stomatal uptake - the complete consumption of the entire an-

sol-

Table 8: NOx-dependent K+ and Mg2+ demand for growth of

entire spruce trees [mol Cat mol-1 NO x] after complete assimilation of the stomatal N0 2 and NO uptake in the needle mesophyll (NO x~ N org)' Both, (i) cation dilution after growth stimulation by NO x' and (ii) an ascending Norg: Cat ratio in spruce tissues (if growth stimulation is absent) is to be avoided in the longterm. Data are amplitudes from young trees (t "" 5 years; first value) up to old trees (t "" 120 years; second value). Results are based on growth scenaria (Slovik, 1996) and tissue contents of healthy spruce trees (Tab. 1). Site elevation [m a.s.!.]

Potassium [mol K+ mol- 1 NO x]

Magnesium [mol Mg2+ mol- 1 NO.]

10m 1000 m

0.200-0.195 0.201-0.198

0.057 -0.065 0.056-0.063

Table 9: «Necessary» N0 2 and S02 concentrations in air (annual means) that cause - after stomatal uptake - a 100 % competition with the annual K+ or Mg2+ uptake from the soil if stimulation of

cation uptake - e. g. after fertilization or liming - is absent in the field. Data are amplitudes from young trees (t "" 5 years; first value) up to old trees (t "" 120 years; second value) if the nutritional status of spruce trees approximates the tissue contents shown in Tab. 1 (= Wiirzburg situation). Site elevation [m a.s.!.]

S02 [nPa Pa- 1 =ppb]

N0 2 [nPa Pa- 1=ppb]

10 m 1000 m

~ 140~140-

95 70

~340-220

10m 1000 m

~200-130

~320-220

Potassium Magnesium

~200-

90

~340-180

~320-180

Table 10: The necessary N0 2 : S02 pollution ratio [nPa Pa- 1 (nPa Pa-1)-I] for the entire K+ or Mg2+ depletion of ageing spruce trees

(after Tab. 9) is a relative measure of the S02: N0 2 toxiciry ratio at equal ambient concentrations in air (common target: annual K+ or Mgz+ budget of spruce trees). Data are amplitudes from young trees (t '" 5 years; first value) up to old trees (t "" 120 years; second value). Site elevation [m a.s.!.]

Potassium, K+ Magnesium, Mg2+ [nPa Pa- 1 (nPa Pa-1)-1]

10 m 1000 m

2.00-2.40 2.10-2.60

1.60-1.65 1.75-1.90

nual K+ or Mg2+ budget of spruce trees. Our data (Table 9) indicate that (70 to ca. 140) nPa SOz Pa-1 (= ppb) are necessary for a complete SOz-dependent K+ consumption (vacuolar K ZS0 4 formation) if K+ contents of spruce tissues are similar to the Wiirzburg situation (cf. Table I), but about (180 to ca. 340) nPa NO z Pa-1 are <
Relative chronic phytotoxicity 01502 and N02 Based on the impact of SOz and NO z on the K+ and Mg2+ budget of entire spruce trees, the relative chronic phytotoxicity of these two trace gases can be compared (Table 9). Ratios of ambient NO z : SOz pollution can be calculated, which would cause the same absolute impact on the cation budget of spruce trees (Table 10). For the K+ budget, the relative phytotoxicity of SOz is 2.0 to 2.6 times higher than an equally high NO z concentration in air. Concerning Mgz+, the SOz toxicity is 1.6 to 1.9 times higher than equally high NO z concentrations in air. Interestingly, chronic NOz-pollution affects the Mg2+ budget relatively more than the K+ budget, but SOz is chronically more phytotoxic than NO z at all site elevations [m a.s.!.] and in any spruce tree age class.

Discussion

Stomatal uptake of the trace gases SOz or NO x (N0 2 + NO) is of course not accompanied by an «equivalent" stomatal cation flux. Thus, irrespective of reductive or oxidative SOz or NO x detoxification in needle mesophyll cells, the stomatal SOz or NO x supply must induce an additional cation demand thar finally must be supplied from the soil. The quantification of this additional cation demand depends on the growth rate of spruce tissues in the field (Slovik, 1996), on their nitrogen, sulphur and cation contents (Table 1) and on the relative participation of oxidative (SOz -+ SOl-) versus reductive (SOZ -+ Sorg) SOz detoxification pathways (cf. Fig. 5 and 6). In the absence of cation fertilization or liming,

The fate of chronic S02 and N0 2 pollution

285

Acknowledgements this additional cation demand can be supplied only from fertile soils, but not at cation-depleted stands. Hence, chronic I am grateful to Prof. Dr. U. Heber and Prof. W. M. Kaiser SOz and NO z pollution can cause mineral deficiency symp- (Wurzburg) for stimulating discussions and advice. This work has toms and they may induce the depression of canopy and root been petformed within the research program of the Sonderforgrowth rates, since root bast and needles contain the highest schungsbereich SFB 251 (TP B 1) of the University of Wurzburg. absolute K+ and Mg2+ contents (cf. Table 1). Consequently, Support by the Deutsche Forschungsgemeinschaft is gratefully ackreduction of root growth (~ mineral and water deficiency) nowledged. and needle growth (~. thinning of the canopy structure) can save cations e.g. for vacuolar sulphate neutralization demands. References Still, the rationale of «spruce decline» proposed here is a tentative attempt to explain observed symptoms in the field (cf. Anonymus, 1989; Anonymus, 1993). NO z usually occurs in ANoNYMus: Dritter Bericht des Fotschungsbeirats WaIdschaden/ Lufrverunreinigungen, FBW Karlsruhe: Kernforschungszentrum too low concentrations in spruce forests (only 8 to 16 nPa 1 (ISSN 0931 - 7805),611 pp. (1989). NO z Pa- ; cf. Slovik et al., 1996 a) for a massive induction of - Waldzustandsbericht der Bundesregierung - Ergebnisse der the here proposed causal rationale. The expected impact of WaIdschadenserhebung - 1993. Bonn (Germany): Referat stomatal NO z uptake on the N org budget of spruce trees lies Offentlichkeitsarbeit und Besucherdienst of the Government of within the natural scattering ofN org analysis data (cf. Table 1). the Federal Republic of Germany (1993). In contrast, the occurring SOz-pollution is high enough at BALAZS, A..: Niederschlagsdeposition in Waldgebieten des Landes some exceptional sites (e.g. in the Erzgebirge; ca. 30 nPa SOz Hessen. Ergebnisse von den Meg-Stationen der «WaldokosyPa- I ppb) for a massive competition mainly with the K+ stemstudie Hessen". Forschungsberichte Hessische Forstliche VersuchsanstaIt. Vol. 11, 168 pp, Hann. Munden: Hessisches budget of spruce. But even then there must be a combination Ministerium fur Landesenrwicklung, Wohnen, Landwirrschaft, of infavourable environmental conditions for the induction of Forsten und Naturschutz (1991). «canopy thinning» symptoms that exceed the natural dynamics of ca. ± 20 % of the stock of needles in healthy canopies. BORTITZ, S.: Physiologische und biochemische Beitrage zur Rauchschadenforschung. 11. Mitteilung: AnaIysen einiger NadelinhaItsMainly the cumulative combination of (i) high 502 concenstoffe an Fichten unterschiedlicher individueller Rauchharte aus trations in air, (ii) short growth periods in the mountains, (iii) einem Schadgebiet. Archiv Forsrwesen 18(2), 123-131 (1%9). poor K+ or Mg2+ depleted soils and (iv) concomitant acid pre- GAMALEI, Y. v., A. J. E. VAN BEL, M. V. PAKHOMOVA, and A. V. cipitation (~ K+ or Mgz+ leaching into the ground water) will SJUTKINA: Effects of temperature on the conformation of the ensynergistically enhance reversible canopy thinning symptoms. doplasmic reticulum and on starch accumulation in leaves with the symplasmic minor-vein configuration. Planta 194, 443-453 The here proposed rationale can explain moderate canopy (1994). thinning symptoms, but spruce decline is not a generally occuring phenomenon in central Europe. The role of wet depo- GRILL, D. and H. ESTERBAUER: Cystein und Glutathion in gesunden und SOrgeschadigten Fichtennadeln. Eur. J. Forest Pathol. sited nitrogen as a dominant cause of «spruce decline» is ob3,65-71 (1973). scure (cf. Table 4), since observed annual nitrogen wet deposiGRILL, D., H. ESTERBAUER, and U. KLOSCH: Effect of sulfur dioxide tion rates usually do not exceed nitrogen loss rates via harveston glutathione in leaves of plants. Environ. Pollution 13, 87-194 ing of trunk wood. Exceptions, e.g. in The Netherlands, may (1979). be admitted, but usually spruce trees will not «grow to death" GRILL, D., H. ESTERBAUER, M. SCHARNER, and CH. FELGITSCH: Efafter excess nitrogen supply (cf. Schulze, 1989). Nevertheless, fect of sulfur-dioxide on protein-SH in needles of Picea abies. «epicuticular» NOx-deposition in natural spruce ecosystems Eur. J. Forest Pathology 10, 263-267 (1980). may trigger harmful consequences if (i) herbaceous plants and HUTTL, R. E: Die Nahrelemenrversorgung geschadigter Walder in Europa und Nordametika. Habilitation thesis, Freiburger Bodenmicroorganisms (incl. pathogens) stimulate their growth and kundliche Abhandlungen (ISSN 0344-2691) 28,440 pp. (1991). (ii) protein-rich (phytopha~e) insects, deers etc. increase their population densities (kgha- ). All these competitive organisms HOvE, K., A. DITTRICH, G. KINDERMANN, S. SLOVlK, and U. HEBER: Detoxification of S02 in conifers differing in SOrtolerance. consume K+ and Mg2+ , which - at least transiently - will beA comparison of Picea abies, Picea pungens and Pinus syLvestris. come unavailable for spruce trees. Most affected by chronic Planta 195.578-585 (1994). K+ and Mg z+ depletion is the growth and turnover of those KAISER, W M., E. MARTINOIA, G. SCHROPPEL-MEIER, and U. HEz spruce tissues, which show high K+ - and Mg + contents BER: Active transport of sulfate into the vacuole of plant cells pro(roots, needles, cf. Table 1). Thus, reduced needle and root vides haIotolerance and can detoxify S02. J. Plant Physiol. 133, growth rates are expected, while trunk wood growth may be 756-763 (1989). largely unaffected, since its K+ and Mg2+ content is low (cf. KAISER, W M., A. P. M. DITTRICH, and U. HEBER: Sulfatakkumulation in Fichtennadeln aIs Foige von S02-Belastung. In: REUTHER, Table 1). Cation deficiency and canopy thinning symptoms M., M. KIRCHNER, and K. ROSEL (eds.): 2. Statusseminar der of less «fit» ecosystem components - here of spruce trees Projektgruppe Bayern zur Erforschung der Wirkung von Ummay be the consequence if there is a soil-defined shortage of weltschadstoffen (PBWU) , Munchen-Neuherberg, 4.-6. Febr. K+ or Mg2+ on a hectare basis. Ir is a well known phenom1991, GSF-Bericht 26/91, 425-438 (1991). enon that N-fertilized grass-lands change their plant species - - - Sulfate concentrations in Norway spruce needles in relacomposition (~ ecosystem drift). Additionally, biodiversity tion to atmospheric S02: a comparison of trees from various forwill be reduced. It may be expected that similar longterm efests in Germany with trees fumigated with S02 in growth chamfects must occur also in N-burdened unmanaged spruce forbers. Tree Physiology 12, 1-13 (1993). ests, but investigation of such time-consuming processes on KANDLER, 0.: Vierzehn Jahre Waldschadensdiskussion. Szenarien und Fakten. Naturwiss. Rundschau 11/94,419-425 (1994). an ecosystem level is a difficult task.

=

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les of Norway Spruce stands (Picea abies) in Central Europe. Plant and Soil 1681169,405-419 (1995). SLOVIK, S., A. SIEGMUND, H. W FUHRER, and U. HEBER: Stomatal uptake of S02, NO x and 0 3 by spruce crowns (Picea abies) and canopy damage in Central Europe. New Phytologist, 132, in press (1996 a). SLOVIK, S.,

A.

BALAzs, and A. SIEGMUND: Canopy throughfall of

Picea abies (L.) Karst. as depending on trace gas concentrations.

Plant and Soil 178(2),255-267 (1996 b). SLOVIK, S., K HOvE, G. KINDERMANN, and W. M. KAISER: S02-dependent cation competition and compartmentation in Norway spruce needles. Plant, Cell and Environment, in press (1996 c). TISCHNER, R., A. PEUKE, D. L. GODBOLD, R. FEIG, G. MERG, and A. HUTTERMANN: The Effect of N0 2 fumigation on Aseptically Grown Spruce Seedlings. J. Plant Physiol. 133,243-246 (1988). VANSELOW, K: Krone und Zuwachs der Fichte in gleichaltrigen Reinbestanden. Forsrwiss. Cbl. 70,705-719 (1951). WELLBURN, A. R.: Why are atmospheric oxides of nitrogen usually phytotoxic and not alternative fertilizers? Tansley Review No. 24, New Phytologist 115,395-429 (1990). WENTZEL, K-F.: Hypothesen und Theorien zum Waldsterben. Forstarchiv 56, 51-56 (1985). WIERSMA, J. H.: A new method of dealing with results of provenance tests. Silvae Genet. 12,200-205 (1963). ZECH, Wand E. Popp: Magnesiummangel, einer der Grlinde fur das Fichten- und Tannensterben in NO-Bayern. Forstwiss. Cbl. 102,50-55 (1983). ZIEGLER, I.: The effect of S02 pollution on plant metabolism. Residue Rev. 56, 79-105 (1975). ZOTTL, H.: Possible causes of forest damage in Germany. CONCAWE Repon 86/61, 55-70 (1986).